No, the game is currently limited to 6 children. You can, however, wait a few "game years" between children so that there can still be a child in the house when the adults are older.

You mentioned that the issue you were having with your game has occurred more than once. It would be a great help if you could try to make it happen again, and tell me step by step what you did, so that I can look into it. You can post your results as a "Reply" to this message or you're welcome to send me a Private Message (PM).